1. Field of the Invention
The present invention relates to surveying rod leveling instruments and more particularly to a device which can be used to check the accuracy of the level attached to a surveying rod.
2. Description of the Prior Art
Levels attached to surveying rods have been used for many years to ensure that the surveying rod is level when measurements are taken. Accuracy is extremely important in the art of surveying because even small errors can result in liability of the surveyor. Over time, however, levels attached to surveying rods can lose accuracy due to jostling and bouncing. It is even possible that new rods have levels that have not been properly calibrated at the factory. It is therefore desirable to have a device which provides a means for ensuring accuracy of the level attached to the surveying rod.
U.S. Pat. No. 4,617,820 issued to Hammond for "Level Calibrating Device" describes a pair of orthogonal horizontal and vertical reference surfaces which are mounted by a bracket to a solid support. An adjustment is provided so that when the mounting bracket is appropriately mounted, the reference surfaces can be adjusted to precisely horizontal and vertical. A plumb bob shows when the surfaces are precisely aligned. The device is then used to check a carpenter,s square or similar instrument. The Hammond device is designed for hand levels and is not suitable or adaptable for the surveying rod levels.
Digricinto, U.S. Pat. No. 2,788,578 discloses a surveyor's target staff with a plumb line for leveling the target in the field. This device is also not suited for surveying rods.
U.S. Pat. No. 3,8789,852, issued to Biondi, describes a vertical positioning device for locating a point at one elevation with respect to a different elevation.
U.K. Patent 1,455,868 discloses a plumb line positioning and holding device used for checking the vertical alignment of top and bottom pivots of a door. U.K. Patent Publication No. 1,455,868 published Nov. 19, 1974, Japanese patent Publication No. 52-17850 published on Feb. 10, 1977 and Japanese Patent Publication No. 62-35219 published on Feb. 16, 1987 all show state of the art for leveling devices.